The present invention relates to a mass spectrometer and a method of operating the same.
A linear trap can perform MSn analysis and has been used widely for proteome analysis, for instance. How the mass dependent ion ejection of ions trapped by the linear trap has been carried out in the past will be described hereunder.
An example of mass dependent ion ejection in a linear trap is described in U.S. Pat. No. 5,420,425. After ions axially inputted have been accumulated in the linear trap, ion selection or ion dissociation is conducted as necessary. Thereafter, a supplemental AC electric field is applied across a pair of opposing quadrupole rods to resonantly excite ions of a particular mass to a radial direction. By scanning a trapping RE voltage, ions can be ejected mass dependently in the radial direction. Since a pseudo harmonic potential formed by a radial quadrupole electric field is used for mass separation, the mass resolution can be high.
Another example of mass dependent ion ejection in a linear trap is described in U.S. Pat. No. 6,177,668. After ions axially inputted have been accumulated in the linear trap, ion selection or dissociation is conducted as necessary. Thereafter, a supplemental AC voltage is applied across a pair of opposing quadrupole rods to excite ions radially. The ions subject to radial resonant excitation are axially ejected by a fringing field developing between the quadrupole rods and an end electrode. The frequency of the supplemental AC voltage or the amplitude value of a trapping RF voltage is scanned. Since a pseudo harmonic potential formed by a radial quadrupole electric field is used for mass separation, the mass resolution can be high.
Still another example of mass dependent ion ejection in a linear trap is described in U.S. Pat. No. 5,783,824. Axially inputted ions are accumulated. A vane lens is inserted between adjacent rod electrodes of a quadrupole rods and a harmonic potential is formed along the linear trap axis by a DC bias applied to the vane lens in respect of the quadrupole rod. Thereafter, by applying a supplemental AC voltage between vane lenses, ions can be excited resonantly and ejected mass dependently in the axial direction. The DC bias or the frequency of the supplemental AC voltage is scanned.
A system for ejecting ions at low energy from a three-dimensional ion trap is described in U.S. Pat. No. 6,852,972. In the method, when ejecting ions from the three-dimensional ion trap, a DC voltage is applied between end caps, and an RF voltage is scanned, so that ions of a higher mass are initially ejected, followed by sequential ejection of ions of lower mass. Since ions can be ejected from the vicinity of an energy minimum point, the spread of ejection energy at room temperature level can be achieved.
Further, U.S. Pat. No. 5,847,386 describes a method of controlling ion motion by inserting electrodes between adjacent rod electrodes of a quadrupole rods to form an axial electric field. Potential difference between the quadrupole rods and the inserted electrodes is utilized to reduce time for ion ejection and to perform trapping.